Delayed extraction experiments using a repulsive potential before ion extraction: evidence of clusters as ion precursors in UV-MALDI. Part I: dynamical effects with the matrix 2,5-dihydroxybenzoic acid |
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Institution: | 1. Biotechnology Institute, School of Environment and Chemical Engineering, Dalian Jiaotong University, Dalian 116028, China;2. Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China;3. School of Environment and Life Science, Kaili University, Kaili 556011, China;4. Dalian Medical University, Dalian 116044, China;5. Shanghai University of Traditional Chinese Medicine, Shanghai 201210, China |
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Abstract: | Delayed extraction experiments were undertaken to precise the dynamical effects involved in the ion formation in ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI). Careful examination of the ion time-of-flight variation with the extraction delay time were performed with a repulsive potential before ion extraction. Depending on the mass of the ion (matrix 2,5-dihydroxybenzoic acid and peptides) and on the repulsing potential, some deviations from the linear relationship between the ion time-of-flight and the delay time were observed. Simulations of the ion time-of-flight clearly show that ions are not directly produced on the target surface but originate from the gas-phase decomposition of higher mass precursors. The size of the precursor, composed of the analyte surrounded by matrix molecules, increases with that of the analyte. Complete desolvation of the cluster-precursor could be likely induced by the high electric field transient during the pulse extraction. The existence of clusters as precursor of the ion production in MALDI highlights a new global frame to explain the analyte protonation in UV-MALDI. |
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